The present invention relates to methods for protecting semiconductor copper bond pad surfaces with ceramic coatings that are sufficiently frangible during ball, wedge or flip chip bonding to obtain metal-to-metal contact between the bonding surfaces and the wires bonded thereto. The method protects the copper bond pads during extended exposure to water and water solutions such as are experienced during sawing.
The use of copper bond pads on semiconductor devices would be an attractive alternative to that of aluminum, were it not for atmospheric contamination of the copper surface, which oxidizes readily to form a coating that is not removable by standard methods of wire bonding machines, and requires the use of fluxes in solder-type interconnects, e.g., flip chip bonding. Present attempts to overcome this problem involve the use of a cover gas that is unavoidably expensive and complex and restricts bond head and work holder movement, or the use of a noble metal or overplating with inert metals which are more costly and can lead to the formation of unwanted intermetallic compounds at the bond pad interface.
U.S. Pat. No. 5,771,157 encapsulates a wedge bond of an aluminum wire to a copper pad with the resin, after the bond is formed. No protection against oxidation is provided to the copper pad prior to wedge bonding.
U.S. Pat. No. 5,785,236 protects a copper bond pad from oxidation with a surface layer of aluminum. This detracts from the advantages sought to be obtained by replacing aluminum bond pads with copper bond pads.
There remains a need for methods by which copper bond pad surfaces may be protected from oxidation prior to wire bonding or flip chip soldering.